Field of the Invention
The present invention relates to an additive used to reduce puddling in inkjet inks. More specifically, the invention relates to a puddling additive having an anionic, polar group and a C6-C30 hydrocarbon tail.
Inkjet printing is a popular alternative for home and office printing due to the low cost of inkjet printers, advances in quality of the printed images, and the relatively noise-free operation. Notwithstanding these advantages, research and development continue in order to improve inkjet print quality while maintaining a reasonable cost for the inkjet printer and the printing process.
To produce high quality images, the inkjet ink must be compatible with the inkjet pen and the print medium. The properties of an optimal inkjet ink include, among others, low puddling, good crusting resistance, good stability, low color-to-color bleed, and rapid dry time. In addition, the inkjet ink must be capable of passing through the inkjet orifice without clogging the orifice or puddling on the orifice plate. The inkjet ink should also permit rapid cleanup of the machine components with minimal effort. Although inkjet inks are known to possess one or more of the foregoing properties, few inkjet inks possess all of these properties because an improvement in one property often negatively impacts another property.
While the overall print quality of inkjet inks is generally high, puddling of inkjet inks still occurs on the orifice plate of the printhead. Inkjet inks comprising magenta dyes are known to exhibit worse puddling than cyan and yellow dyes. Puddling occurs when the ink that is ejected through the orifices does not reach the print medium. Instead, the inkjet ink collects on an outer surface of the orifice plate or puddles adjacent to the edge of the orifice. This occurs when ink drops exiting the orifices leave behind minute amounts of ink on the orifice plate around each orifice. The extent of the puddling varies from a few, small drops of ink to the formation of large puddles on large portions of the orifice plate. Large puddles partially or completely block the orifices and cause missing nozzles, false low decap values, or changes in the trajectory of the ink drops. The change in trajectory results in the ink drop not hitting its targeted pixel center, which creates printing errors on the media and reduces the quality of the printed image.
Various solutions to address the problem of puddling have been proposed. Some solutions propose modifying the printhead or pen to reduce puddling, while other solutions modify the inkjet ink composition. For example, a coating of hydrophobic material is applied to the printhead to reduce its wettability and, thereby, reduce puddling. However, this modification to the printhead is costly. A combination of pen architecture and modifications to the inkjet ink composition has been suggested to reduce puddling.
Other proposed modifications to the inkjet inks include adding anionic and nonionic surfactants to the inkjet ink. Similarly, others have proposed adding a first surfactant and a second surfactant to reduce puddling. The first surfactant has a hydrophilic-lipophilic balance (xe2x80x9cHLBxe2x80x9d) value of 1.5 units lower than the second surfactant. Additional modifications include adding salts to the inkjet inks. However, adding salts or surfactants causes reliability and materials interaction issues because the additives cannot be used with all dyes or ink vehicles. In addition, adding surfactants or salts negatively affects desirable properties of the inkjet inks.
It would be desirable to reduce puddling of inkjet inks by using additives that are effective in low amounts and do not negatively affect other properties of the inkjet inks. In addition, it would be desirable to use additives that are effective in many types of, ink vehicles.
A puddling additive used in an inkjet ink is disclosed. The puddling additive comprises an anionic, polar group and a C6-C30 hydrocarbon tail. A method of reducing puddling in inkjet inks is also disclosed. The method comprises adding a puddling additive to the inkjet ink.
A set of inkjet inks is also disclosed. Each inkjet ink comprises a dye, an aqueous ink vehicle, and a puddling additive, which comprises an anionic, polar group and a C6-C30 hydrocarbon tail.